Generally, shallow trench isolation (STI) helps to prevent electrical current leakage between adjacent semiconductor devices. In STI, one or more trenches, i.e., the shallow trenches, may be etched into a surface of a substrate and then filled with a dielectric material, such as silicon dioxide. The trenches may be used to isolate semiconductor devices that may then be formed in the trenches. The dielectric material may help to reduce electrical current leakage between adjacent semiconductor devices within the same trench or across different trenches.
Due to electric field enhancement at edges of the trenches, it may be easier to form a conducting channel at a lower voltage. This may effectively reduce the threshold voltage (VT) of the semiconductor devices in the integrated circuit. Therefore, STI has become a widely used technique for improving integrated circuit performance in complementary metal oxide semiconductor (CMOS) integrated circuits.